One of the known prior systems of insulating pipes requires the use of polyurethane foam and has the following disadvantages:
The heater is very sensitive to the humidity. If humidity infiltrates the insulating substance, an hydrolysis occurs. This chemical reaction is followed by release of hydrochloric acid which may affect the foam support, namely the pipes themselves.
The insulation thus obtained by this prior art system is also affected by heat and cannot be used at temperatures exceeding 90.degree. or 100.degree. C.
The use of such a process involves the emission of chemical substances that may be very hazardous to the people and thus generates labor problems.
Considering the possible variation of the volume of foam obtained from the initial foam generating substance, and the fact that this volume of foam is dependant upon the ambient temperature, the foam may generate a high pressure around the walls of the pipes, and that pressure may be detrimental to these pipes.
It is impossible to design fittings that would provide good seal with the insulation. In addition, fittings and couplings are expensive and require a significant amount of work for their installation. Besides with time, the seal of the insulation with the fittings will deteriorate.
The thermomechanical properties of polyurethane foam is rated very low, and therefore it is inferior to the thermomechanical properties of epoxy foam.
In any case, the average life of the conduits thus obtained does not exceed 5 to 6 years.